Protecting the Ischemic Spinal Cord During Aortic Clamping

Abstract

Infrarenal circumaortic occlusion devices were operatively placed in 74 New Zealand white rabbits. Two days after operation the animals were randomly assigned to one of seven treatment groups: I, control, n = 23; II, halothane, n = 8; III, thiopental, n = 12; IV, ketamine (30 mg/kg intravenously), n = 6; V, halothane+hypothermia, n = 8; VI, thiopental+hypothermia, n = 12; VII, ketamine+hypothermia, n = 5. In each group, the infrarenal aorta was occluded for 21 minutes. Final neurologic recovery after restitution of blood flow was graded as acute paraplegia, delayed paraplegia (neurologic deficit developing after initial recovery), or normal. Halothane alone was of no benefit. Hypothermia with any anesthetic was completely protective and reduced neurologic deficits to 0% compared with 91% in controls (p less than 0.05). Thiopental and ketamine treatment each reduced acute paraplegia to 17% (as compared with 61% in controls) and increased delayed paraplegia from 30% in controls to 75% and 50%, respectively (p less than 0.05 for thiopental, p = 0.10 for ketamine). The authors interpret the increase in delayed deficits and decrease in acute deficits as being the result of partial spinal cord protection. These findings document that this model of spinal cord ischemia is sufficiently sensitive to identify interventional treatments that protect the ischemic spinal cord.

Effects of Hypothermia on Blood Flow and Neural Activity in Rabbit Spinal Cord during Postischemic Reperfusion.

“…This did not happen in the present study because laminectomy, which prevents an increase in cerebrospinal fluid pressure, was performed to fix stimulating and recording electrodes. Studies have been carried out to estimate the effects of medications, such as thiopental, ketamine, lidocaine, naloxone, magnesium, methylprednisolone, and tissue factor pathway inhibitor, on transient spinal cord ischemia [37][38][39][40]. Some of these medications showed beneficial effects on spinal cord exposed to ischemia/ reperfusion in animal experiments, but none is accepted as a clinical treatment for patients with spinal cord ischemia or patients who undergo aortic reconstructive surgery.…”

Protection in Animal Models of Brain and Spinal Cord Injury with Mild to Moderate Hypothermia

“…In 1986, Robertson et al showed that moderate hypothermia (338C) increased the duration of ischemia required to produce neurological deficits in rabbits (Robertson et al, 1986). Hypothermia has been found to improve outcome in several animal models of ischemic SCI, including pigs (Colon et al, 1987;Strauch et al, 2004), rabbits (Naslund et al, 1992;Wakamatsu et al, 1999;Tetik et al, 2002), and dogs (Berguer et al, 1992;Tabayashi et al, 1993) Various new methodologies producing local cooling including epidural cooling techniques have also provided positive results (Yoshitake et al, 2007). In a study by Malatova et al (1995), an epidural cooling technique provided evidence that deep spinal cord hypothermia provided some degree of protection following a regional ischemic insult.…”

Effect of graded hypothermia (27 degrees to 34 degrees C) on behavioral function, histopathology, and spinal blood flow after spinal ischemia in rat.

“…Flow is improved with cerebrospinal fluid drainage, 15 and because hypothermia decreases cerebrospinal fluid pressure, improved residual flow may provide sufficient nutritive flow for a relatively prolonged occlusion period before neuronal energy failure. 8 Second, hypothermia is known to diminish clotting which would retard the development, if any, of the evolution of microemboli. Third, ischemia might evoke the release of active factors, such as thromboxane B 2 , which alter vascular tone.…”